This invention relates generally to inflatable restraint systems and, more particularly, in one aspect to the type of inflator known as a hybrid inflator and the treatment of gases therein and in another aspect to the treatment of gas generated by inflatable restraint system inflators.
Many types of inflators have been disclosed in the art for inflating an air bag for use in an inflatable restraint system. One type involves the utilization of a quantity of stored compressed gas which is selectively released to inflate the air bag. Another type derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the air bag. In a third type, the air bag inflating gas results from the combination of a stored compressed gas and the combustion products of a gas generating material. The last mentioned type is commonly referred to as an augmented gas or hybrid inflator.
Hybrid inflators that have been proposed heretofore have, in general, been subject to certain disadvantages. For example, the burning of the pyrotechnic (gas generating) and initiation materials in such inflators invariably results in the production of particulate material. The use of such a particulate-containing inflator emission to inflate an air bag can in turn result in the particulate material being vented out from the air bag and into the vehicle.
Typically, the particulate material is variously sized and includes a large amount of particulate within the respirable range for humans. Thus, the passage of the gas borne particulate material into the passenger compartment of the vehicle, such as via conventional air bag venting, can result in the undesired respiration of such particulate material by the driver and/or other passengers which in turn can cause consequent respiratory problems. Also, such particulate can easily become dispersed and airborne so as to appear robesmoke and thereby result in the false impression that there is a fire in or about the vehicle.
It has also been proposed to screen the gaseous emission coming from the pyrotechnic portion of such hybrid inflators. For example, the above-identified U.S. Pat. No. 5,131,680 discloses the inclusion of a circular screen "128" between the body of pyrotechnic material and the orifice through which the pyrotechnically produced emission is passed to the pressurized gas-containing chamber of the hybrid inflator.
Also, U.S. Pat. No. 5,016,914 discloses the inclusion of a metal disk having a plurality of suitably sized openings therein. The disk is disclosed as functioning to trap large particles such as may be present in the generated gas.
Such techniques of filtering or screening the gaseous emission of the pyrotechnic section of the hybrid inflator prior to contact with the stored, pressurized gas of the inflator generally suffer such as from undesirably slowing or preventing the transfer of heat to the stored gas from the relatively hot generated gas and particulate material. In general, such a transfer of heat to the stored gas is desired in hybrid inflators in order to produce desired expansion of the gas. Consequently, the slowing or preventing of desired heat transfer can result in a reduction in the performance of the inflator. Also, the screening or filtering of particulate at this location within the inflator can undesirably effect gas flow within the inflator. For example, such treatment can undesirably restrict the flow of gas out of the pyrotechnic chamber, causing the pressure inside the pyrotechnic chamber to increase and thereby increase the potential for structural failure by the pyrotechnic chamber.
The above-identified U.S. Pat. No. 5,016,914 also discloses constraining gas flow to a tortuous path whereby additional quantities of relatively large particles produced by combustion of the gas generating material are separated from the commingled gases as the gases flow toward the inflatable vehicle occupant restraint. As disclosed, various component parts of the vehicle occupant restraint system cooperate to form the described tortuous path. These component parts include the openings in the container which direct the gas into an outer cylindrical diffuser, the container itself which preferably contains gas directing blades positioned therein as well as burst disks to control the flow of the gas generated by ignition of the gas generating material. The patent also discloses that in a preferred embodiment, a coating material, e.g., a silicone grease, is coated onto the inner surface of the container to assist in the fusing of particles thereto rather than allowing the particles to rebound into the nitrogen gas jet stream.
Such surface coatings, however, generally suffer in several significant aspects with respect to effectiveness and functioning when compared, for example, to the use of a filter to effect particulate removal.
First, as the nature of such fusion or adhesion of particles onto a coating is a surface phenomenon, the effectiveness of such removal is directly related to the amount of available surface area. In practice, such a surface coating provides a relatively limited amount of contact surface area and, further, the effectiveness of such surface treatment typically is decreased as the available surface area is occupied.
Also, though such an internal surface coating may be of some use in the fusing of solid particles, such a coating would normally be relatively ineffective in trapping liquid phase particles. Furthermore, the process of condensation of liquid phase particles in an inflator normally involves a transfer of heat to the subject contact surface. In the case of such a surface coated with such a grease, such a transfer of heat could undesirably result in the off-gassing of the coating material, e.g., production of gaseous byproducts of the coating material, which in turn would undesirably contribute to the toxicity of the gases emitted from such an inflator.
In addition, the effect of the flow of gases within the inflator can raise concerns about the use of inflators which utilize such coatings. For example, the impingement onto such a coating of the hot combustion gases produced within an inflator would normally tend to displace the coating material, particularly since such coatings tend to become softer at elevated temperatures.
Thus, even for the short time periods associated with the operation of such devices neither exclusive nor primary reliance is made by this patent on the use of such a coating to effect particle removal.
There is a need and a demand for improvement in hybrid inflators to the end of preventing, minimizing or reducing the passage of particulate material therefrom without undesirably slowing or preventing heat transfer to the stored, compressed gas while facilitating proper bag deployment, in a safe, effective and economical manner.
The present invention was devised to help fill the gap that has existed in the art in these respects.
In addition and as described above, inflators, particularly those which house a combustible gas generating material whether alone or in conjunction with a stored gas as in hybrid inflators, have in the past utilized various grades of fine metal screens to effect emission filtration.
Unfortunately, partially as a result of the costs associated with the manufacture of such screens, such screen materials can be relatively costly.
Also, depending on factors such as the looming and crimping processes employed, individual wires in such metal meshes can experience significant movement relative to adjacent wires and, as a result, detrimentally effect the strength of the resulting wire mesh material.
In addition, the edges of wire meshes or screens used in inflator filter assemblies are susceptible to permitting particulate-containing gas generant effluent to pass therethrough and circumvent the main particulate-removing components of the filter assemblies. Such circumvention, also termed "blow-by," can permit undesired and unacceptable amounts of particulates to escape with the inflation gas out of the inflator.
Furthermore, the nature of wire meshes or screens prevents the production of a one piece material which has a first portion without openings, e.g., such as a border or edge, and a second portion with openings, e.g., such as a central region.
In general, inflator filters include several components which cooperate to perform various functions or treatments, such as, provide for the cooling, flow redirection and filtering (e.g., particulate removal) of or from the contacting stream. Also, one or more filter assembly components can serve to provide structural support for other filter components such as those that could not otherwise withstand the operating conditions (e.g., temperatures, pressures, and/or flow rates) to which it would be subjected to in use.
Thus there is a need and a demand for improvement in the components and materials used in inflator filter assemblies to reduce cost as well as to improve production, operational and assembly options and capabilities.